Material loads, such as structural steel, for example, may be delivered to warehouses for processing on flatbed trucks. After the material load is offloaded, there may be a need to move the materials between various parts of the warehouse for different types of processing. For example, in the case of processing structural steel, one area of the warehouse may be used for drilling, and another area of the warehouse may be used for welding. Accordingly, there may be a need to move the structural steel members between various areas of the warehouse.
Currently, structural steel members may be moved by wrapping a pair of chains around portions of the structural steel member, and connecting an end of the chains to a hoist. This system, however, requires that the center of gravity of the structural steel members be located before lifting the load. If the structural steel member is lifted off-center, the structural steel member will not be level. Accordingly, if the structural steel member is not level, a danger exists that the structural steel member may slide out of the chains and drop from its lifted position. Therefore, upon discovering that the structural steel member is lifted out of level, an operator of a hoist lowers the structural steel member and moves the position of the chains in an attempt to lift the structural steel member in a level position. This process is generally repeated until the center of gravity is located. Use of such a system may be time consuming.
U.S. Pat. No. 3,942,834 to Kawaguchi discloses a lifting device for lifting structural steel members. The lifting device includes a pair of opposing grappling arms that are pivotally connected to support plates. More specifically, the weight of the body of the lifting device causes the lifting arms to initially be in an extended position. As the lifting device is lowered, a structural steel contact member engages the top of a flange of the structural steel member to pivot the grappling arms inwardly so that the structural steel member may be lifted. After the structural steel member is lifted using the Kawaguchi '834 lifting device, however, the structural steel member may not be level. Accordingly, it may be necessary to lower the grappling arms, disengage the grappling arms from the structural steel member and re-position the grappling arms along the structural steel member so that the structural steel member may be lifted and moved in a level position. Again, this process may be time consuming.
U.S. Pat. No. 3,455,593 to Moro discloses a lifting device including a pair of opposing lifting tongs. Each lifting tong includes a pair of opposing grappling arms that may be moved between engaged and disengaged positions responsive to movement of a hinged plate. More specifically, the hinged plate engages a plate guide, and is moved between a locked and an unlocked position within a plate guide. The Moro '593 lifting device requires that the grappling arms be moved to a disengaged position before engaging the object to be lifted. Accordingly, use of the lifting device may also be time consuming, and may require additional labor to lift and move a material load.
U.S. Pat. No. 3,709,548 to Hogshead discloses a leveling sling for carrying and leveling an elongate load. The sling includes a pulley system through which a plurality of cables may be passed so that the cable length may be readily adjusted to level the elongate load. More specifically, the leveling sling requires an initial adjustment of the cables to roughly level the load before it is lifted, and a small adjustment of the cables after the load has been lifted to thereby level the load after it has been lifted.
U.S. Pat. No. 5,037,151 to Kameyama et al. discloses a lifting device including a pair of opposing actuators that may be operated pneumatically, hydraulically or electrically. More specifically, the lifting device includes a pair of extendable guide arms that connect to a lower portion of an elongate beam. Lifting slings are connected to the ends of the guide arms. The actuators are in communication with a remote controller, which may be used to send a signal to extend and contract the guide arms. Accordingly, each of the opposing guide arms are selectively controlled by remote control so that a user may move the guide arms inwardly or outwardly, thereby adjusting the position of the lifting slings to accommodate various sized loads.